Image intensifier secondary emissive matrix internally coated to form a converging lens



y 12, 1966 a. w. MANLEY ETAL 3,

IMAGE INTENSIFIER SECONDARY EMISSIVE MATRIX INTERNALLY COATED TO FORM A CONVERGING' LENS Filed April 15, 1964 mvamoas BRIAN WILLIAM MANLEY klggg ADAMS United States Patent 3,260,876 IMAGE INTENSIFIER SECONDARY EMISSIVE MATRIX INTERNALLY COATED TO FORM A CONVERGLNG LENS Brian William Manley, Burgess Hill, John Adams, East Grinstead, Derek Washington, Redhill, and Michael Brannen, Burgess Hill, England, assignors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Apr. 15, 1964, Ser. No. 359,855 Claims priority, application Great Britain, Dec. 6, 1963, 13,205/63 1 Claim. (Cl. 313-68) With intensification of electron beams by secondary emission the spread of the beam is increased. A narrow beam of electrons having struck once or several times a secondary-emission electrode will cover a larger surface on the collecting screen than corresponds to the initial sectional area of the beam. This is also the case, when one or more tubular channels for guiding the flow of electrons is(are) used, which flow is intensified in the channels by secondary emission. It is known to use a large number of channels, together occupying the whole sectional area of the beam, as secondary-emission intensifiers in cathode-ray tubes in which the electrons are emitted by a photo-electric cathode, in which case the electron density in the beam is locally proportional to the brightness of the image projected onto the photocathode producing the emission of electrons. The common target points of the electron beams passing through each of the channels produce the photo cathode image on a fluorescent screen, which is arranged opposite the exits of the channels. Apart from the gain in brightness of the picture on the screen, there is a reduction in definition due to the increase in spread of electrons.

The invention relates to a cathode-ray tube having an electron source and a fluorescent screen, said tube comprising a matrix passing electrons and arranged parallel to the fluorescent screen and made of material of poor electrical conductivity, said matrix being provided with closely arranged narrow passages extending in the direction of the electron paths, the two surfaces of said matrix, where the passages open out, being coated with electrically conductive layers, the passages having secondary-emissive surfaces.

The invention has for its object to improve the definition of the picture produced by the electron beams on the phosphor screen. In accordance with the invention the passages are coated, on the exit side of the electrons, over a small part of their lengths, with electrically conductive material which is integral with the coating on the same side of the surface of the matrix passing the electrons.

The inner rims of the surface coating in the passages affect the potential distribution along the axes of the passages so that spherical, equipotential planes are produced, which may be compared with the field distribution in electron lenses and which thus have a concentrating effect on the course of the emerging electrons.

The invention will be described with reference to the drawing, in which FIG. 1 shows diagrammatically part of the matrix passing the electrons.

FIG. 2 is an elevation of part of said matrix.

FIGS. 3 and 4 shown electron beams with and without the use of the invention.

FIG. 5 shows an image reproducing tube and FIG. 6 shows an image intensifying tube comprising a matrix passing the electrons.

Said matrix consists of insulating material or of a kind of material having a certain degree of conductivity for electrons, but not too great a conductivity. The flow of electrons must remain within certain limits. If too great 3,260,876 Patented July 12, 1966 a flow is allowed to pass, heating is produced, so that the properties of the material may change. An excessively small flow is attended with a non-uniform distribution of the electric field. Glass having a resistance of the order of 10 to 10 ohm cm. is quite suitable.

The body is provided with the passages 2. The number of passages is at a maximum, for example about 10 passages/(m The two sides of the body 1, with the exception of the openings of the passages, are coated with metal layers 3 and 4. The fluorescent screen 5 consists of a layer of luminescent material, applied to a support 6 of glass, which may form the wall of the envelope of a tube. The intermediate surface between the glass wall and the screen is conductive.

The electrons, concentrated in a beam 7, move from the left-hand side and part of them strikes the coating 3, whereas the other electrons continue their way through the passages 2. They do not travel rectilinearly, but along curved paths, which terminate at the inner surface 8. The secondary emission involves electron multiplica tion, so that each input electron corresponds to a plurality of electrons on the exit side of the passages. FIG. 3 gives an impression of the spacial section of such emerging electron beams 9, which have a considerable spread, which is disadvantageous for the definition of the picture.

The peripheral coating or conducting rim 10 of FIG. 4 of the passages 2 has a concentrating effect on the electrons, which are united to form beams 9 of a narrower spacial section.

The electrons are accelerated by electric fields produced by voltages from voltage sources 11 and 12. The voltage source 11 is connected to the conducting coatings 3 and 4 and the voltage source 12 supplies the acceleration voltage between the coating 4 and the conducting layer of the fluorescent screen 5.

The concentration of the electrons on the exit side of the passages in the presence of the conducting rim 10 is based on the difference produced between the potential distribution along the surface of the passage and the distribution in the axis thereof. As a result curved equipotential planes are produced, the effect of which may be compared with the effect of an electron lens. The conducting layer must be formed by a material having no secondary-emissive properties, preferably aluminium. The conducting coatings may be obtained by vapour-deposition and the conducting rims on the inner sides of the passages may be obtained by directing the vapour jet obliquely to the surface and by moving the vapour source along a circle around the axis of the screen.

The cathode ray-tube of FIG. 5 is a television display tube comprising a cathode system 13, which produces a directional electron beam, which is deflected so that the point of impact moves along the target screen 5. Parallel to the screen 5 there is arranged the matrix 1, which allows the electrons to pass, The system of deflecting members 14 is shown diagrammatically.

The cathode ray tube of FIG. 6 is an image intensifier comprising an envelope 15 having two flat end walls 16 and 17, the wall 16 being the support of a photo-electric cathode 18 and the wall 17 being the support of the fluorescent screen 5. An object 19 is projected by means of a lens 20 onto the photo-cathode 18, so that an electron image is formed, the electrons of which move from the photo cathode 18 towards the target screen 5. Between these two elements there is arranged the matrix 1 providing the secondary-emissive intensification.

What is claimed is:

A cathode-ray tube comprising a source of electrons and a fluorescent screen, and having, parallel to the fluorescent screen, a matrix for passing the electrons and made of material of poor electrical conductivity, having closely arranged, narrow passages extending in the direction of the electron paths, the two surfaces of said matrix, where the passages open out, being coated with electrically conductive layers, said passages having secondary-emissive surfaces, characterized in that on the exit side of the electrons the surfaces of the passages are coated over a small part of their length with electrically conductive material which is integral with the coating on the same side of the matrix.

No references cited.

DAVID J. GALVIN, Primary Examiner.

V. LAFRANCHI, Assistant Examiner. 

